Regioisomerism in cationic sulfonyl-substituted [Ir(C^N)₂(N^N)]⁺ complexes: its influence on photophysical properties and LEC performance

Abstract

A series of regioisomeric cationic iridium complexes of the type [Ir(C^N)2(bpy)][PF6] (bpy = 2,2'-bipyridine) is reported. The complexes contain 2-phenylpyridine-based cyclometallating ligands with a methylsulfonyl group in either the 3-, 4- or 5-position of the phenyl ring. All the complexes have been fully characterized, including their crystal structures. In acetonitrile solution, all the compounds are green emitters with emission maxima between 493 and 517 nm. Whereas substitution meta to the Ir-C bond leads to vibrationally structured emission profiles and photoluminescence quantum yields of 74 and 77%, placing a sulfone substituent in a para position results in a broad, featureless emission band, an enhanced quantum yield of 92% and a shorter excited-state lifetime. These results suggest a larger ligand-centred ((3)LC) character of the emissive triplet state in the case of meta substitution and a more pronounced charge transfer (CT) character in the case of para substitution. Going from solution to the solid state (powder samples and thin films), the emission maxima are red-shifted for all the complexes, resulting in green-yellow emission. Data obtained from electrochemical measurements and density functional theory calculations parallel the photophysical trends. Light-emitting electrochemical cells (LECs) based on the complexes were fabricated and evaluated. A maximum efficiency of 4.5 lm W(-1) at a maximum luminance of 940 cd m(-2) was observed for the LEC with the complex incorporating the sulfone substituent in the 4-position when operated under pulsed current driving conditions.

Investigating Intracellular Localisation and Cytotoxicity Trends for Neutral and Cationic Iridium Tetrazolato Complexes in Live Cells

“…Furthermore, the excited‐state lifetime of [Ir( ppy ) 2 ( TziQn )] is significantly longer than that of [Ir( ppy ) 2 ( TzQn )] (Table ). These results suggest the presence of a more dominating charge transfer character for the emission of [Ir( ppy ) 2 ( TzQn )] . On the other hand, the excited state of [Ir( ppy ) 2 ( TziQn )] seems to be strongly influenced by LC character .…”

“…These results suggest the presence of a more dominating charge transfer character for the emission of [Ir( ppy ) 2 ( TzQn )] . On the other hand, the excited state of [Ir( ppy ) 2 ( TziQn )] seems to be strongly influenced by LC character . To confirm this assumption, we performed time‐dependent density functional theory (TD‐DFT) analysis on [Ir( ppy ) 2 ( TzQn )] and [Ir( ppy ) 2 ( TziQn )] (see the Supporting Information).…”

Highly Stable and Efficient Light-Emitting Electrochemical Cells Based on Cationic Iridium Complexes Bearing Arylazole Ancillary Ligands

“…This behavior is typical of emissive states with a large 3 LC character. 51,52 The emission color of the complexes in solution goes from yellow-orange ( Complexes [4] 6 ] is similar to that previously reported by Sunesh et al 40 The Φ PL of complex [1] 6 ], a biexponential fit was used to determine an average lifetime value of 316 ns (see Table S4 in the Supporting Information for details). The lower Φ PL and shorter τ values recorded for [4][PF 6 ] and [5][PF 6 ] determine the higher nonradiative decay rate constants obtained for these two complexes.…”

Sulfonyl-Substituted Heteroleptic Cyclometalated Iridium(III) Complexes as Blue Emitters for Solution-Processable Phosphorescent Organic Light-Emitting Diodes

“…It has been established previously that functionalizing the phenyl ring of FIrpic 1 with an electron-withdrawing group at C3 (i.e., between the two F atoms) induces a blue shift in emission: examples are cyano, sulfonyl, phosphoryl, and perfluoroalkyl carbonyl substituents . The present work focuses on sulfonyl groups, which have only rarely been incorporated as substituents on C^N cyclometallating ligands in either neutral or ionic complexes. With the exception of complex 11 , which has been reported previously by Fan et al using a different method to introduce the p -toluenesulfonyl substituent, to our knowledge the sulfone-containing complexes studied in this work have not been synthesized previously.…”